This proposal is designed to further our knowledge of the respiratory use of molecular hydrogen by Salmonella typhimurium. The long-term outcome of these exploratory studies is to assess the feasibility of targeting this process via metal chelation in order to prevent enteric bacterial-mediated diseases. Infection by the enteric human pathogen Salmonella typhimurium result in millions of cases of diarrheal illness annually and the prospect of the malevolent introduction of enteric pathogens into food or water supplies makes them an NIAID category B biodefense priority concern. The pathogen has excellent capacity to split molecular H2 and use the low potential electrons in a respiratory manner (with O2 as the terminal acceptor). It is proposed to identify the respiratory proteins used by the pathogen to metabolize molecular hydrogen. Characterizations of the role of H2 oxidation will be approached by comparing mutant strains in each of the hydrogenases for H2 affinities associated with each H2-binding enzyme, for their individual ability to facilitate amino acid transport, and to reduce a cytochrome-containing respiratory chain. The affects of nickel chelators (i.e. nickel starvation conditions) on the expression of each individual hydrogenase will be assessed by studying the mutant strains. The major research areas covered by this proposal include both pathogen biology and exploratory therapeutics development to combat infectious disease. Salmonella bacteria result in millions of cases of human diarrheal disease annually. Inhibiting growth of the bacterium within animal hosts is the long-term goal of this work.